The present invention relates generally to a centrifuge device which is capable of centrifuging a blood sample contained in a blood tube and also reading the blood component layers formed in the blood tube as a result of the centrifugation. More particularly, the present invention relates to a centrifuge device having a movable optical reader device that is capable of moving with respect to the blood tube to optically read the blood component layers in the entire centrifuged blood sample while the blood sample is being spun by the rotor of the centrifuge device, and further having an indexing mechanism which rotates the blood tube in the rotor about an axis substantially corresponding to the longitudinal axis of the blood tube, while the rotor is spinning the blood tube, so that the component layers can be read by the optical reader device from different locations about the circumference of the blood tube. The centrifuge device further has detectors for detecting the centrifugation of the rotor to control the reading of the blood tube, and the loading and unloading of the blood tube in the rotor.
As part of a routine physical or diagnostic examination of a patient, it is common for a physician to order a complete blood count for the patient. The patient's blood sample may be collected in one of two ways. In the venous method, a syringe is used to collect a sample of the patient's blood in a test tube containing an anticoagulation agent. A portion of the sample is later transferred to a narrow glass sample tube such as a capillary tube. The open end of the sample tube is placed in the blood sample in the test tube, and a quantity of blood enters the sample tube by capillary action. The sample tube has two fill lines at locations about circumference, and the volume of blood collected should reach a level in the sample tube between the two fill lines. In the capillary method, the syringe and test tube are not used, and the patient's blood is introduced directly into the sample tube from a small incision made in the skin. In either case, the sample tube is then placed in a centrifuge, such as the Model 424740 centrifuge manufactured by Becton Dickinson and Company.
In the centrifuge, the sample tube containing the blood sample is rotated at a desired speed (typically 8,000 to 12,000 rpm) for several minutes. The high speed centrifugation separates the components of the blood by density. Specifically, the blood sample is divided into a layer of red blood cells, a buffy coat region consisting of layers of granulocytes, mixed lymphocytes and monocytes, and platelets, and a plasma layer. The length of each layer can then be optically measured, either manually or automatically, to obtain a count for each blood component in the blood sample. This is possible because the inner diameter of the sample tube and the packing density of each blood component is known, and hence the volume occupied by each layer and the number of cells contained within it can be calculated based on the measured length of the layer. Exemplary measuring devices that can be used for this purpose include those described in U.S. Pat. Nos. 4,156,570 and 4,558,947, both to Stephen C. Wardlaw, and the QBC.RTM. "AUTOREAD" centrifuged hematology system manufactured by Becton Dickinson and Company.
Several techniques have been developed for increasing the accuracy with which the various layer thickness in the centrifuged blood sample can be determined. For example, because the buffy coat region is typically small in comparison to the red blood cell and plasma regions, it is desirable to expand the length of the buffy coat region so that more accurate measurements of the layers in that region can be made. As described in U.S. Pat. Nos. 4,027,660, 4,077,396, 4,082,085 and 4,567,754, all to Stephen C. Wardlaw, and in U.S. Pat. No. 4,823,624 to Rodolfo R. Rodriquez, this can be achieved by inserting a precision-molded plastic float into the blood sample in the sample tube prior to centrifugation. The float has approximately the same density as the cells in the buffy coat region, and thus becomes suspended in that region after centrifugation. Since the outer diameter of the float is only slightly less than the inner diameter of the sample tube (typically by about 80 .mu.m), the length of the buffy coat region will expand to make up for the significant reduction in the effective diameter of the tube that the buffy coat region can occupy due to the presence of the float. By this method, an expansion of the length of the buffy coat region by a factor of about 4 and 20 can be obtained. The cell counts calculated for the components of the buffy coat region will take into account the expansion factor attributable to the float.
Another technique that is used to enhance the accuracy of the layer thickness measurements is the introduction of fluorescent dyes (in the form of dried coatings) into the sample tube. When the blood sample is added to the sample tube, these dyes dissolve into the sample and cause the various blood cell layers to fluoresce at different optical wavelengths when they are excited by a suitable light source. As a result, the boundaries between the layers can be discerned more easily when the layer thickness are measured following centrifugation.
Typically, the centrifugation step and the layer thickness measurement step are carried out at different times and in different devices. That is, the centrifugation operation is first carried out to completion in a centrifuge, and the sample tube is then removed from the centrifuge and placed in a separate reading device so that the blood cell layer thickness can be measured. More recently, however, a technique has been developed in which the layer thickness are calculated using a dynamic or predictive method while centrifugation is taking place. This is advantageous not only in reducing the total amount of time required for a complete blood count to be obtained, but also in allowing the entire procedure to be carried out in a single device. Apparatus and methods for implementing this technique are disclosed in the aforementioned copending applications of Stephen C. Wardlaw entitled "Assembly for Rapid Measurement of Cell Layers", Ser. No. 08/814,536 which has issued as U.S Pat. No. 5,889,581 and "Method for Rapid Measurement of Cell Layers", Ser. No. 08/814,535 which has issued as U.S. Pat No. 5,888,184.
In order to allow the centrifugation and layer thickness steps to be carried out simultaneously, it is necessary to freeze the image of the sample tube as it is rotating at high speed on the centrifuge rotor. This can be accomplished by means of xenon flash lamp assembly that produces, via a lens and a bandpass filter, an intense excitation pulse of blue light energy (at approximately 470 nanometers) once per revolution of the centrifuge rotor. The pulse of blue light excites the dyes in the expanded buffy coat area of the sample tube, causing the dyes to fluoresce with light of a known wave length. The emitted fluorescent light resulting from the excitation flash is focused by a high-resolution lens onto a linear CCD array. The CCD array is located behind a bandpass filter which selects the specific wavelength of emitted light to be imaged onto the CCD.
The xenon flash lamp assembly is one of two illumination sources that are focused onto the sample tube while the centrifuged rotor is in motion. The other source is an array of light-emitting diodes (LEDs) which transmits red light through the sample tube for detection by the CCD array through a second band pass filter. The purpose of the transmitted light is to initially locate the beginning and end of the plastic float (which indicates the location of the expanded buffy coat area), and the full lines. Further details of the optical reading apparatus may be found in the aforementioned copending applications of Michael R. Walters entitled "Inertial Tube Indexer" Ser. No. 08/032931, and in the aforementioned copending application of Bradley S. Thomas entitled "Flash Tube Reflector with Arc Guide" Ser. No. 09/032925.
Since it is desirable to read the layers in the centrifuge blood sample while the centrifuged blood sample remains in the centrifuge, it is also desirable to insure that the readings are as accurate as possible. It is therefore necessary to accurately monitor the orientation of the rotor in which the blood sample is being centrifuged in relation to the optical reading device, so that the optical reading device will perform the readings at the exact times that the centrifuged blood sample is in the reading area. Since the rotor is spinning at several thousands of revolutions per minute, it is necessary to synchronize the reading perfectly with the rotation of the rotor so that the sample can be read without slowing down the rotation speed.
As described above, it is also desirable to rotate the sample tube about its longitudinal axis, so that readings can be taken at different locations about the circumference of the blood tube, thus providing a more accurate measurement of the lengths of the blood component layers in the centrifuged blood sample. Details of an indexing apparatus for performing this function may be found in the aforementioned copending application of Michael R. Walters entitled "Inertial Tube Indexer" Ser. No. 09/032,931. Additionally, it is also desirable to be capable of reading different portions of the blood sample at different times. Furthermore, because the readings are based on light being transmitted through the centrifuged sample and light that is emitted from the centrifuged sample in response to excitation light irradiated onto the centrifuge sample, it is desirable to prevent light of unwanted wavelengths from being detected to improve the readings being taken by the optical detector.
Accordingly, a continuing need exists for an apparatus which is capable of centrifuging a blood sample stored in a sample tube, and taking accurate measurements of the component layers of the centrifuged blood sample while the sample tube remains in the centrifuge device and continues to be rotated by the rotor of the centrifuge device.